1. Field of the Invention
The present invention relates to an improved method of manufacture of EL lamps, and to electroluminescent lamps produced thereby.
2. Description of the Related Art
Electroluminescent ("EL") lamps commonly comprise a laminated assembly including phosphor material, a dielectric layer, and front and rear electrodes, with leads for applying an alternating electric field across the electrodes, to cause the phosphor to emit radiant (luminescent) energy, e.g., in the visible light spectrum, infrared, or ultraviolet spectrum.
In such EL lamps, the phosphor material and dielectric layer between the electrodes, generally maintain the two electrodes in separated relationship to one another, thereby preventing them from short-circuiting.
For such purpose, and to electrically isolate the phosphor layer from the rear electrode, it has been conventional practice to pattern the rear electrode conductive material, since the front electrode typically is formed as a continuous metallization layer of appropriate size and shape of the supporting substrate, e.g., a polymeric film such as Mylar.RTM. film. Such patterning of the rear electrode may be carried out by silk-screening, to apply the electrode as a conductive metalpolymer paste in a specific final shape configuration which will achieve the desired electrical isolation of the phosphor layer from the electrical field. Alternatively, the metallized front electrode supported by the substrate could be subjected to chemical, laser or mechanical metal-removal processes prior to applying the subsequent lamp layers, but same are typically for the manufacture of a pre-determined final lamp shape configuration.
Accordingly, it would be a significant advance in the art to provide a methodology for the ready manufacture of variable final EL lamp configurations by the selective removal of the rear electrode metal layer from a continuous, pre-printed EL lamp blank, to achieve the desired electrical isolation pattern of the phosphor layer from the electrical field imposed by means of the front and rear electrodes of the lamp with an associated power supply.
Relative to the state of the art in the field of the invention, relevant references are described below.
U.S. Pat. Nos. 5,276,382 and 5,332,946 teach the use of a thin "line of interruption" in which a portion of the continuous conductive material of the substrate supported front electrode, in the form of a line between 0.005 and 0.010 inches wide, is removed by laser ablation, directly or though a mask, prior to the application of selectively pre-applied lamp layers. The line of interruption creates an isolated island that is electrically discontinuous from the remainder of the front electrode, and provides the electrically isolated lead attachment area and/or the final end product lamp edges.
By this arrangement, a lead making contact with the outer rear electrode can be attached to a region previously electrically isolated from the underlying main body of the front electrode. Short circuiting between the front and rear electrodes will not occur within this electrically isolated region when performing lead attachment to the outer electrode e.g., as a result of a crimping-type lead connector being applied to the laminated structure. The prior art also teaches that the front electrode main body becomes isolated from the edges of the final lamp shape by ablating a line of interruption prior to applying the remaining lamp layers.
The method disclosed in U.S. Pat. Nos. 5,276,382 and 5,332,946 is used during the lamination layering process and manufacture of EL lamps. Electrically isolated sections of the front electrode are outlined by the "line of interruption", followed by subsequent layering. The configuration of the electrically isolated sections is determined by the pre-selected rear electrode pattern based upon a pre-determined final lamp configuration. The remaining separation layers are laminated over the electrically isolated front layer followed by the pre-patterned rear electrode. The product EL lamp is then cut to its final pre-determined shape by some mechanical means.
U.S. Pat. No. 5,702,565 to Wu et al. uses a similar but slightly more sophisticated front electrode "line of interruption" ablation technique to form multiple electrically isolated "address lines" in the front electrode layer of an EL laminate. These parallel address lines are formed by directing a laser beam through the front (transparent) side of a fully layered EL laminate onto the top surface of the underlying layer of the EL laminate. Typically, the underlying layer includes the dielectric layer(s) and the rear electrode layer. The laser device must be precisely adjusted to pass through each of the individual overlying layers, which include a transparent top layer, transparent front electrode layer and the phosphor layer. The laser beam directly ablates a portion of the top surface of the underlying layer creating sufficient heat energy to vaporize a thin line of the transparent front electrode layer. The laser beam is line indexed over the front side of the EL laminate forming over 200 parallel and electrically isolated lines per inch distance.
Although the method disclosed in U.S. Pat. No. 5,702,565 has the advantage of being a postproduction EL laminate process, it does not apply to the removal of large sections or regions of an electrode layer. Additionally, the technique of directing a laser beam through multiple overlying layers to ablate the top surface of the underlying layer is expensive and requires exacting precision. The exact properties of the each material layer and their thickness must be known as well as the precision and resolution of the laser in order to avoid explosive delamination of the intervening layers and to minimize interdiffusion between the layers.
Mechanical devices have also been proposed to remove a narrow line of the conductive material to form multiple electrodes. See, for example, U.S. Pat. No. 4,534,743. One means disclosed for removing a portion of the conductive material is the application of a solvent to the material, followed by removal of the material portion with a wire brush, thereby creating a "narrow groove" in the conductive material, providing at least two laterally spaced electrodes.
Alternatively, a precision saw blade might be used. The size of the narrow groove is approximately 0.127 millimeters (0.005 inch).
The method disclosed in U.S. Pat. No. 4,534,743 of wire brushing the conductive material uses the edges of the wire brush to remove the conductive material, with the bristles of the wire brush being perpendicular to the axis of the shaft of the tool used to direct the brush. The patent describes the use of a shielding device to construct a thin line cut, and to protect the functional rear electrode material. This method, however, may undesirably result in removing material at different depths, since it is difficult to control the edges of the brush with precision. This in turn can cause damage to the underlying substrate, thereby weakening the lamp. Further, the narrow groove formed by the wire brushing could permit an electric arc to traverse the groove, thereby causing a short circuit. The method disclosed is suitable for producing a split rear electrode lamp with twice the voltage drop of the conventional parallel electrode lamps. The method, however, does not lend itself to complex lamp configurations and end product final lamp shapes.
Another technique for removing a portion of the conductive material on an electrode is disclosed in U.S. Pat. No. 5,223,687. This patent teaches the creation of a fine pattern on the electrode, thereby creating multiple electrodes suitable for illuminating multiple lighted areas within a liquid crystal display. A metal electrode is employed, having a needle-like tip through which a voltage is applied between such metal electrode and the conductive material, thereby etching a narrow groove in the conductive material. The size of the area in which the conductive material is removed extends up to 10 microns around the contacting area.
Similar to the result in U.S. Pat. No. 5,702,565 discussed above, U.S. Pat. No. 5,223,687 teaches the formation of multiple parallel lines extending across the electrode using a metal electrode with multiple needle-like tips to remove thin lines of conductive material. The drawbacks to this approach include the difficulty of accurately controlling an electrode with a small needle tip that concentrates the electric charge, as well as removing the resulting scattered etched particles from the electrode substrate. Furthermore, the use of significant voltages may create safety hazards. In addition, the removal of an area of the conductive material, which is 10 microns in width, of itself, may not prevent electrical arcing, and consequently such processing may still result in significant risk of short-circuiting in the use and operation of the lamp constructed from such electrode. As is the case with most of the prior art discussed, this method of electrode removal is applied during the manufacturing process of the EL lamp and is not practical for use with a completely layered EL laminate.
Another approach for removing an area of conductive material is disclosed in U.S. Pat. No. 4,745,334. This patent teaches cutting out a portion of the rear electrode in the vicinity of the area in which lead terminals are attached to the front electrode of the lamp. The lead terminals are attached using a printed board. This method is employed in order to apply heat to the terminals of the lamp at an area distant from the lamp. This method requires the removal of a portion of the entire front electrode layer and supporting substrate, e.g., polymeric film. Accordingly, the portion of the lamp article having the front electrode cut away introduces a significant variation in thickness to the lamp, which may be detrimental from a packaging or aesthetic standpoint. Further, the cutting operation introduces a processing step which increases the complexity of the manufacturing process, and which may result in damage to the metal coating incident to the severing of the portion to be excised, in connection with the stresses thereby imparted to the electrode layer at distances beyond the cut-out portion. Such stresses may result in delamination of the metal film on the substrate, with consequent adverse effect on the performance of the resultant lamp article.
Thus, most of the prior art approaches remove a portion of the conductive material as an integral part of the EL material layering process. The end result being that the desired electrode pattern is pre-determined based upon the defined manufacturing process. The final El lamp shape is also a function of the configuration of the pre-printed layers that make up the EL laminate. The only prior art method approach used to remove a portion of the conductive material on post-laminated EL lamp material is highly specific and not designed to remove relatively large regions of electrode material. Further, the prior art emphasis on removal of conductive material from an electrode structure typically has focused on the front electrode and associated "lit" surface of the EL lamp, and the art has not addressed satisfactorily metal removal from the rear electrode for electrical isolation of the phosphor material. Finally, none of the prior art approaches incorporate a technique for selectively forming the final EL lamp shape from a stock EL laminate material, or EL "blank" sheet. An EL blank represents the fully layered EL laminate material, with the same "blank" being usefully employed for any of a multiplicity of designs.
The present invention is directed to, inter alia, an improved EL lamp and appertaining method of manufacture.